Introduction Impulse oscillometry is a non-invasive method used to measure airway impedance. There is increasing interest in utilising frequency dependence of airway resistance/reactance to study small airways disease in asthma. We examined frequency dependant behaviour in severe asthma and the response to deep inspiration and bronchodilators.
Methods 27 healthy controls (C) (Mean (sem) age; 48.4 (2.2), Sex M:F; 9:18, post-bronchodilator FEV1% predicted; 108.2 (2.8)%) and 66 GINA stage 4–5 severe asthmatics (A) (Mean (Sem) age; 54.1 (1.4), Sex M:F; 31:35, post-bronchodilator FEV1% predicted; 81.02(2.7)%), were recruited from Glenfield Hospital, UK. Impulse oscillometry (IOS) was performed at 5–35 Hz, with impulses triggered every 0.2 s for 150 s, at (1) baseline (base) (2) immediately after five deep breaths (TLC-RV) (pdb) (3) 15 min after 400 mcg inhaled salbutamol (pbd). Markers of total (R5) and large airway (R20) resistance, and frequency dependant behaviour of resistance (R5-R20) and reactance area (AX) were evaluated.Triplicate measurements of 150 s were performed in 18 randomly selected asthmatics from our cohort to assess repeatability.
Results Impedence measurements were highly repeatable (an intra-class correlation of 0.9) in the triplicate series. We observed asignificant increase in frequency dependence of both resistance (R5-R20) and reactance (AX) after deep inspiration in asthma, but not in healthy controls, which was reversed by the use of a bronchodilator (Abstract P123 Figures 1A–D). In addition R20 increased in both severe asthma and healthy controls after deep inspiration.
Conclusions Deep inspiration significantly increased frequency dependence of resistance and reactance in severe asthma suggesting that the small airways may be related to the aberrant deep inspiratory response in severe asthma.